1. Field of the Invention
This invention relates to a light beam scanning system, and more particularly to a light beam scanning system which combines a plurality of laser beams emitted from a plurality of semiconductor lasers into a single laser beam and scans an object with the combined leaser beam.
2. Description of the Prior Art
There have been used various light beam scanning systems in which a light beam is deflected by a light deflector to scan a recording medium to record thereon various information or to read information recorded thereon. In such light beam scanning systems, it is known to use a semiconductor laser as the means for generating the light beam. The semiconductor laser is advantageous over other light sources such as a gas laser in that it is small in size and inexpensive, and has low power consumption. Further, in the case of the semiconductor laser, the light beam can be directly modulated by changing the driving current.
On the other hand, the semiconductor laser can continuously output 20 to 30 mW at most and accordingly, it has been difficult to use the semiconductor laser in light beam scanning systems in which a high energy light beam is required, e.g., a light beam scanning system for recording on a recording medium having a low sensitivity such as a metal film, an amorphous film or other draw materials.
When certain kinds of phosphors are exposed to a radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light, light is emitted by the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor, and a sheet provided with a layer of the stimulable phosphor is generally referred to as a stimulable phosphor sheet. As disclosed in Japanese Unexamined patent publication Nos. 55(1980)-12429, 55(1980)-116340, 55(1980)-163472, 56(1981)-11395, 56(1981)-104645 and the like, it has been proposed to use a stimulable phosphor sheet in a radiation image recording and reproducing system. Specifically, the stimulable phosphor sheet is first exposed to a radiation passing through an object to have a radiation image stored thereon, and is then scanned with stimulating rays such as a laser beam which cause it to emit light in the pattern of the stored image. The light emitted by the stimulable phosphor sheet upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a visible image on a recording medium such as a photographic film or on a display device such as a cathode ray tube (CRT). In such systems currently available, the stimulating rays must have a high energy and accordingly, it has been very difficult to use a semiconductor laser as a source of the stimulating rays.
It will be possible to obtain a scanning light beam having a high energy by combining laser beams emitted by a plurality of semiconductor lasers into a single laser beam. (In this case, the laser beams may be combined between the laser sources and the object to be scanned or on the object to be scanned.) When the stimulating rays for stimulating the stimulable phosphor are obtained by combining laser beams, laser beams having the same wavelengths will be used so that the combined laser beam has a wavelength suitable for stimulating the stimulable phosphor. However, there is a problem that a slight difference in wavelength between the laser beams to be combined generates beat in the combined laser beam, whereby the amount of the scanning light can be changed from picture element to picture element to adversely affect the accuracy in recording or reading.